Although the AT2 receptor has been known since the 1980s, much less is known about its biological function than the angiotensin II type 1 (AT1) receptor, which has been studied for its functional effects on vasoconstriction, aldosterone release and cardiovascular growth [Wexler et al., 1996]. However, more recently the AT2 receptor has been implicated in the differentiation and regeneration of neuronal tissue [Steckelings et al., 2005; Chakrabarty et al., 2008], cell proliferation and angiogenesis [Clere et al., 2010] and maintenance of bone mass [Izu et al., 2009].
AT2 receptor antagonists have also recently been associated with the treatment of pain, particularly inflammatory pain [WO 2007/106938] and neuropathic pain [WO 2006/066361], two types of pain which are difficult to treat or relieve. Impaired nerve conduction velocity is also associated with nerve damage and has been implicated in peripheral neuropathies, Carpel Tunnel Syndrome, ulnar neuropathy, Guillian-Barré Syndrome, fascioscapulohumeral muscular dystrophy and spinal disc herneation. Impaired nerve conduction velocity can result in diminished reflex responses and altered peripheral sensation such as parathesia and in some cases pain and AT2 receptor antagonists have been shown to restore nerve conduction velocity [WO 2011/088504].
While there are effective therapies for treating nociceptive pain, inflammatory and neuropathic pain are often resistant to these therapies. In addition, current therapies of neuropathic pain, inflammatory pain, impaired nerve conduction velocity and other types of pain that are difficult to treat, have serious side effects, for example, cognitive changes, sedation, nausea and in the case of narcotic drugs, tolerance and dependence. There is a need for further therapies that treat or prevent neuropathic pain, inflammatory pain, impaired nerve conduction velocity and other painful conditions that are currently difficult to treat.
Cell proliferation and angiogenesis are important biological functions in normal tissue. However, uncontrolled cell proliferation and angiogenesis can lead to tumors and other proliferative disorders. While there are some effective chemotherapies available for tumors, many result in unpleasant side effects and/or have high toxicity for normal cells. Further therapies for reducing or preventing abnormal cell proliferation in a controlled manner are required and AT2 receptor antagonists have been shown to have antiproliferative activity [Clere et al., 2010].
Osteoporosis is a significant problem in older populations, especially in post-menopausal women. Current therapies for osteoporosis rely on calcium supplementation. However, the control of bone formation and bone resorption is complex and further therapies for improving bone mass are required and AT2 receptor antagonists have been shown to increase bone mass [Izu et al., 2009].
The role of the AT2 receptor in modulating neuronal outgrowth and associated effects of AT2 receptor antagonists on reducing neuronal outgrowth, indicates that AT2 receptor antagonists may be useful therapeutics in diseases characterized by aberrant nerve regeneration [Chakrabarty et al., 2008].
The present invention is predicated in part on the discovery of heterocyclic azetidine and pyrrolidine compounds that have AT2 receptor antagonist activity.